1.Field of the Invention
This invention relates to a lead frame material formed of a copper alloy for use in a resin sealed type semiconductor device having high adhesion strength to an epoxy resin sealing material and leads for a semiconductor device.
2. Prior Art
Conventionally, transistors, IC's, and further, LSI's are known in general as semiconductor devices. Among them, e.g. a resin sealed type IC is produced by the following known method, which comprises the essential steps of:
(a) preparing, as a lead frame material, a Cu-alloy strip having a plate thickness of 0.1 to 0.3 mm; PA1 (b) forming from the above lead frame material by etching or punching a lead frame suitable in shape for an IC to be produced; PA1 (c) effecting heat adhesion of semiconductor chips of Si, Ge, etc., each having a high purity to predetermined locations of the lead frame, by the use of an electrically conductive resin, such as an Ag paste, or alternatively soldering or Au-brazing the semiconductor chips through plated layers formed of Au, Ag, Pd, Ni, Cu, or an alloy thereof, which have been formed by plating partly or entirely on one side surface of each of the semiconductor chips and the lead frame material; PA1 (d) connecting the semiconductor chips to the lead frame by means of bonding wires, such as an extra fine wire of Au and an extra fine wire of Cu; PA1 (e) subsequently sealing, for protection, the semiconductor chips, the bonding wires, and the lead frame with the semiconductor chips mounted thereon, by the use of an epoxy resin as a sealing material; and PA1 (f) finally cutting off border portions of the lead frame between adjacent chip-mounted portions thereof, and plating fixture legs of the lead frame with an Sn-Pb alloy soldering material according to the customary dipping technique, electrical method, or the like.
In producing the above-mentioned resin sealed type semiconductor device, various types of Cu alloys are used as lead frame materials. Among them is known a Cu alloy having a chemical composition consisting essentially, by weight percent (hereinafter referred to simply as "%"), of 1 to 4% Ni, 0.1 to 1% Si, 0.1 to 2% Zn, 0.001 to 0.05% Mg, and the balance of Cu and inevitable impurities. It is also known that this Cu alloy is excellent in strength as well as solder-heat exfoliation resistance, so that it now finds wide practical applications.
On the other hand, the development of semiconductor devices with greater integration is conspicuous in recent years, and accordingly, the above-mentioned resin sealed type semiconductor devices are forced to operate under severe conditions. However, the conventional lead frame material formed of the above-mentioned Cu alloy for forming the sealed type semiconductor devices does not have satisfactory adhesion strength to an epoxy resin as a sealing material, so that exfoliation is likely to occur after use for a relatively short time period. As a result, ambient air (especially moisture) penetrates into a slight gap formed between the lead frame and the sealing material, thereby causing erosion of components of the semiconductor device. Thus, the conventional lead frame materials have unsatisfactory reliability.